Automatic strip gauge control for a rolling mill



May 31, 1966 L. F. sTRlNGER AUTOMATIC STRIP GAUGE CONTROL FOR A ROLLING MILL Filed April 29, 196s 7- Sheets-Sheet l mQZQOmm Z- MEE. Ov Om ON OONN L emNm- LIAISSIWB BAIlOBddB May 31, 1966 L. F. sTRlNGER 3,253,438

AUTOMATIC STRIP GAUGE CONTROL FOR A ROLLING MILL BYTQWM/ 240@ j@ l ATTORNEY May 31, 1966 L. F. STRINGER AUTOMATIC STRIP GAUGE CONTROL FOR A ROLLING MILL Filed April 29, 1965 '7 Sheets-ShedI 5 f42 CARO-READER SCREwDOwN POSITION CONTROL I COMPUTER z BS 3I\ s? :35 wIOTH THICKNESS LQ THICKNESS WIDTH GAUGE GAUGE GAUGE GAUGE l l I I I 2 I 2 o '6 I I 40 S I I4 3G TEMPERATURE I TEMPERATURE MANUAL GAUGE I8 GAUGE INPUTS 22 MILL MOTOR FIG-4- SPEEO CONTROL s CONvENTIONAL MILL MOTOR APPARATUS :I: 0.4 O 54 INCI-I BACKUP ROLL U) D O 3" 59 INCI-I BACKUP ROLL o D. ROLL BENOING n .J 5 0.2

E F |g.5 EE

5 Oil FRAME,SCREw,NUT IL; ROLL FLATTENING,AND 5 BOTTOM SUPPORT UI l o l I I I l I I l I E 2O 4o GO BO IOO |20 PRODUCT WIDTH-INCHES May '31, 1966 AUTOMATIC Filed April 29, 1963 L. F. sTRINGI-:R 3,253,438

STRIP GAUGE CONTROL FOR A ROLLING MILL 7 Sheets-Sheet 4 4 'r2 INCH BACKUP RoLL 3 DIAMETER s4 INCH 2 :2- O D.

2 g FI g. 6. d z

INCHES FROM CENTER oF MILL o I l I I I l 2o 4o eo eo INCHES RoLL CRowN 0.0i

l '2 T '3T 4 T5 ,G .7 T PAssIN-HI PASS@ PAssIN+II PAss(N) ENTRY GUAGE DELIVERY GAUGE- INCHES PASS@ May 31, 1966 L F. sTRlNGER AUTOMATIC STRIP GAUGE CONTROL FOR A ROLLING MILL '7 Sheets-Sheet 5 Filed April 29, 1963 L. F. STRINGER AUTOMATIC STRIP GAUGE CONTROL FOR A ROLLING MILL May 31, 1966 7 Sheets-Sheet 6 Filed April 29, 1963 May 31, 1966 L. F. sTRlNGER AUTOMATIC STRIP GAUGE CONTROL FOR A ROLLING MILL '7 Sheets-Sheet '7 Filed April 29, 1963 Nm J r L 52mm 55u28 l mm2 S 2 @on .25252 555mm 55.32 f Kim Kim Q2 Q2 20.52 ozmz NY w02@ m62@ mm2@ lx m2225225 m2222512? m o wom o l o m Il U mm2@ m52@ Imm wwmzv; mmmzv I l u sms nl @i A .65.200 .65200 .6528 202.50@ Alll mmtoo AI 29.53@ A ESQO AT 29h50@ Al zsonzmmom zaonzmmow 2 o mmom 2 o m United States Patent O 3,253,438 AUTMA'IIC STRIP GAUGE CNTROL FR A ROLLING MILL Loren IF. Stringer, Clarence, N.Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a

corporation of Pennsylvania Filed Apr. 29, 1963, Ser. No. 276,269 11 Claims. (Cl. 72-12) This application is a continuation-in-part of an earlier patent application, Serial No. 225,350, filed September 2l, 1962, by the same inventor and assigned to the same assignee.

The present invention relates in general to automaticstrip gauge or thickness control for a strip rolling mill, and more particularly to automatic gauge control for succeeding operations of a rolling mill based upon previous operations of the same mill.

In the automatic control of metal rolling mills, it is well known to employ card programmed sequencers and even online computer devices. However, a very difiicult control area has been relative to the use of roll force signals to control delivery workpiece gauge or thickness in the operation of rolling mills. A large variety of different incoming slab dimensions and slab temperatures as well as desired delivery dimensions, in addition to a considerable variety of rneta'l alloys, must be handled. The rolling mill operator has the further problem of determining the proper screwdown adjustments tor compensate for roll bending to produce a substantially flat delivered workpiece shape from the mill.

It is an object of this invention to provide an improved method and apparatus for better controlling a rolling mill to effect an improved rolling mill operation regarding the better control of the screwdown roll opening adjustment or draft of the material passed through the rolling mill to improve the product yield therefrom.

It is a different object of the present invention to provide an improved quality product from a rolling mill by better controlling the loading of the mill during each pass or succeeding stand such that there is provided a more uniform shape and more accurate nal delivery thickness of the material rolled.

It is an additional object of the present invention to provide improved control of a metal rolling mill by an iterative feed forward of control information from preceding passes or stands to succeeding passes or stands to provide the desired quality product without overloading the mechanical and electrical equipment, in accordance with the roll position during each pass or stand being held substantially constant, the mill motor torque being held below a predetermined value to prevent overheating of the mill motor, the motor armature current being limited for a similar purpose, and the allowable-reduction in any given pass or stand in terms of draft percentage or actual reduction being held less than a predetermined value determined by the known characteristics of the material being rolled.

In accordance with the present invention, an on-line computer is operatively coupled to control a metal rolling mill, such as a reversing plate mill or -a multiple stand mill. The computer is supplied for each pass or stand, as input data, the incoming slab dimensions, the desired delivery dimensions, and the material index according to the metal alloy or grade. In addition, the desired rolling speed and a predetermined screwdown position are supplied as input data.

The computer is then operative for a reversing plate mill to control the rolling program regarding hoW many initial passes and turns are required and the thickness of the plate delivered from each pass to obtain the desired final plate Width, and either one of a prescheduled numice ber of passes or how many subsequent passes are required and the screwdown setting for each such pass asrequired to obtain the desired final plate thickness. For a multiple stand mill, the screwdown setting for the next stand is determined and corrected. As each pass is completed, information is fed back to the computer for the roll separating force, the drive motor torque, the computed delivery plate thickness and the delivery plate length for the determination of the next succeeding screwdown setting to give the desired roll position for the next succeeding pass. Thus, this information utilization for the desired iterative feed forward screwdown control enables the computer to modify as desired the screwdown or drafting operation ou successive passes or stands.

The present invention teachings will provide the maximum permissible production Within the capabilities of the involved mechanical and electrical equipment of the metal rolling mill and within the end purpose of achieving the desired quality of the finally produced rolled plate.

In a hot metal workpiece rolling mill, a large and red hot workpiece is passed successively between large cylindrical rolls to reduce the thickness and determine the width of the final product thereof.

As the thickness of the workpiece becomes less and less, the mill spring effect becomes of greater importance. Thusly, it becomes desirable to calculate and predict what the roll force will be for each succeeding pass between work rolls and then determine the screwdown setting for that pass to compensate for the resultant spring elongation or stretch of the rolling mill. Sensing devices -are used to measure the actual roll separating force, and

comparisons with the predicted roll force will determine any difference or error for use to update the involved control equations to allow more accurate operation of the mill for particularly the last few and more critical passes or stands.

The above and other objectsand advantages of the present invention will become apparent in view of the following description taken in conjunction with the drawings.

FIGURE l shows an information flow diagram for the present computer operation;

FIG. 2 is a curve showing calculated effective thermal emissivity of a workpiece;

FIG. 3 is a curve showing calculated versus recorded temperature decay in a steel workpiece rolled in a reversing plate rolling mill;

FIG. 4 shows adiagrammatic illustration of a fourhigh reversing plate rolling mill and screwdown control apparatus for controlling the rolled thickness of a workpiece in accordance with the teachings of the present invention;

FIG. 5 shows a curve illustrating the total mill stretchy for ll million pounds roll separation force as a function of product width from 25 inches to 130 inches wide for both a 54 inch backup roll and a 59 inch backup roll;

FIG. 6 provides a curve illustrating the distribution of crown across the face of the rolling mill where the diameter of the Work roll center is .0l inch greater than the diameter at the edge of the work roll;

FIG. 7 is a curve showing an illustrative plot of roll separation force in millions of pounds as a function of delivery workpiece thickness;

FIG. 8 is a functional showing of the present computer operation;

FIG. 9 is a curve illustrating roll force as a function of the stretch of the mill stand frame;

FIG. l() is a diagrammatic showing of the present computer apparatus applied to a continuous rolling mill;

FIG. ll is a modified diagrammatic showing of the present invention applied to a continuous tandem rolling mill; and

FIG. 12 is a curve plot illustrating the work strip temperature changes measured at succeeding stands of the rolling mill.

The flow diagram of FIG. l illustrates how the rolling is controlled in accordance with the present teachings with particular emphasis on the use of the available information. The first step for a reversing mill is to perform the schedule calculation and determine the desired number of passes and the delivery thickness for each pass. The computer does this based on a set of empirical equations and constraints obtained from past experience for the particular grade of metal being rolled and dependent upon the nominal delivery temperature. It is assumed that the schedule will be calculated in groups of passes such that the operation of the mill will not be delayed by the schedule calculations per se. For a continuous mill, the number of stands will determine the number of passes. Before each pass through the mill is made, the roll force is predicted and the roll opening is thereby set to compensate for calculated mill stretch. The pass is then performed and measurements are made of the actual roll separating force and the actual motor torque. The latter information is used to update the force and torque equations in such a way as to compensate for variations in alloying of the metal and in the temperature. A test is made by the computer after each pass through a pair of rolls to determine whether because of low predictions the expected motor torque or roll force for the next pass will be too high such that a recalculation is desired. If the equations have predicted the roll force or motor torque at too high a value for any particular pass, the computer recalculates the schedule as permitted to increase the number of passes for a reversing mill or to alter the scheduled stand settings for a continuous mill.

FIGURE 2 illustrates a plot of the variation of effective emissivity of the workpiece as a function of temperature and plate thickness. A trend toward the increase of effective emissivity with decreasing plate thickness is readily noticed. The curves shown in FIG. 2 were obtained for slabs with a thickness range of 0.85 inch to 6 inches.

Workpiece temperature is difiicult'to establish by direct measurement because the available temperature sensing devices which are used to scan the workpiece surface before and after a pass can only indicate the surface temperature and this is not an accurate measurement because the surface of the workpiece is often hidden by clouds of steam and scale. Further, since heat is transferred from the workpiece to the surrounding environment, a temperature gradient exists within the workpiece. The interior regions of the workpiece are at a higher temperature than the surface. The roll force is sensitive to temperature of the workpiece and will be a function of the internal workpiece temperature as well as the surface temperature. Therefore, even if the surface temperature could be measured accurately, some sort of correction factor would have to be used to establish the mean temperature of the workpiece. The uncertainties in measuring the workpiece surface temperature accurately and consistently under actual mill operating conditions, together with the need for some sort of correction factor to obtain average temperature, placed added emphasis on the need to develop an equation for predicting the decay of the average temperature in workpieces during rolling.

In FIG. 3, there is shown a temperature decay curve illustrating predicted temperature values based upon empirical observation of rolling mill operation and actually recorded values taken for a pilot mill.

Several factors must be considered before this data can be utilized in the actual operation of a rolling mill, for example, the effect of water sprays to change the level of the effective emissivity should be considered. However, practical emissivity curves can be provided for all workpieces contemplated to be passed through the rolling mill under actual mill operation conditions, and once these are established the temperature decay can be predicted during any phase of the actual rolling.

In FIG. 4 there is diagrammatically shown one form of control apparatus suitable for operation in accordance with the teachings of the present invention. The rolling mill 10 is illustrated as a reversing mill and includes an upper roll 12 and a lower roll 14, an upper backup roll 16 and a lower backup roll 18. A mill motor 20 is operative with the lower roll 14 and in turn is controlled by a conventional mill motor speed control 22 which is operative to feedback actual operation signals to the computer 24 and to, in turn, receive a mill motor speed control signal from the computer. In addition, the mill motor speed control 22 is operative for speed regulation with the conventional mill control apparatus 26 presently well known to persons skilled in this particular art.

A screwdown position control 28 is operative with a screwdown motor 30 for controlling the separating force and thereby the opening or setting between the roll members 12 and 14. The screwdown position control is operative to supply a roll setting position feedback signal t0 the computer 24, while the computer 24 is operative to supply a screwdown positioning control signal to the screwdown position control 28. An entry thickness gauge 31 is opertive with the strip or workpiece 32 entering the rolling mill 1t). l This entry thickness gauge 31 as well as the delivery thickness gauge 34 may comprise X-ray gauges or the like and are operative with the computer 24 for supplying actual workpiece `thickness signals when desired. An entry temperature gauge 36 and a delivery temperature gauge 33 are operative with the computer 24 for supplying workpiece temperature indication signals when desired. Strip width measuring gauges 33 and 35 are operative with the computer 24, as is a roll speed measuring transducer 39. A roll force sensing transducer 37 such as a well known strain gauge is provided to supply a roll force signal to the computer 24. The manual inputs 40 indicated as operative with the computer, as Well as the card reader 42, can be utilized to provide desired and known in advance control signals to the computer 24 in accordance with predetermined and known workpiece and rolling mill practice parameters.

FIG. 5 shows the total mill stretch for 11 million pounds of roll separating force as a function of product width from 25 inches to 130 inches wide and respectively for 54 inches and for 59 inches diameter backup rolls. The information shown in FIG. 5 is preferably stored in the computer memory in the form of a suitable equation so that product width and the roll diameter can be used to derive the mill spring constant M for controlling the rolling operation as will be later described.

FIG. 6 shows the distribution of crown of the roll members across the face of the mill Where the center of the work roll diameters is .0l inch greater than the diameter at the edge of the work roll. In this regard, roll crown is provided by the diameter at the center of the roll being greater than the diameter at the ends of the roll and is used to at least partially compensate for the effect of roll bending. FIG. 6 shows the distribution of crown across the face of the mill, and the total roll separating force required to produce a plate of uniform thickness for varying widths using the .0l inch crown. The upper line in FIG. 6 shows the force required when using a 72 inch backup roll, and the lower curve shows the force required when using a 64 inch backup roll. As the width of the plate being rolled decreases, the force required to produce a plate of uniform thickness also reduces. As an example, the lower curve shows that the difference in crown between the middle of the plate and the edge of the plate when rolling a 112 inch wide plate 56 inches from the center line of the mill to the edge of the plate is .005 inch per roll. The upper lines show that with this width a force of 1.5 million pounds would be required for 64 inch backup rolls and 2.7 million pounds for 72 inch backup rolls. In actual practice, it is usual to work the mill with roll separating forces higher than those shown in the illustration to produce a plate which is slightly thicker in the middle than along the edges. This results in a stable rolling operation with no tendency for the plate to move to one side of the mill or to the other. Once the desired amount of crown is determined using the iinal plate thickness, this same percent crown should be used on all of the thin passes so that the elongation down the middle of the plate wil be the same as that along the edges of the plate. If this is done, the plate will lie at on the table even though it is slightly thicker in the middle than on the edges. This requirement is not necessary when the piece is thick because there is enough side flow of material in the bite of the roll and the plate has enough mechanical strength to cause it to lie flat even though there is some difference in the -apparent elongation of the edges compared to the center.

The computer considers four different limits in determining the draft to be taken in each pass. These are inches draft, percent draft, motor torque and roll separating force. In general, the input plate temperature, width and thickness cause one of these four limits to determine the draft than can be taken. The most important of these, particularly on the latter passes, is roll separating force. By properly controlling the roll separating force, the plate shape can be controlled and mechanical equipment can be protected. The following table shows the last eight passes in an illustrative schedule where the plate is being reduced from 1.8 inches down to .25 inch thick.

The drafting was performed in a way to control the crown in the linal product to a desired value of 2.2%. The earlier passes were limited by torque Iand percent draft. For this reason, it is not possible to maintain the same amount of crown when the product is thick as compared to the thinner passes. Passes 4 and 5 approach the desired amount of crown and passes 6, 7 `and 8 give the exact percent crown desired. Since this is a percentage figure, the roll force required is slightly higher for the thicker passes and the thickness of the plate in the middle as compared to the edges as expressed in inches is greater for the thicker products. This type of drafting practice causes the elongation down the middle of the plate as compared to the elongation along the edge of the plate to be vsubstantially the same, particularly on the latter passes Where shape is critical. y

In the general gauge control procedure in accordance with the present invention, the computer controls the piece thickness or gauge by predicting the roll separating force in accordance with the mill spring parameter for each pass and using the nominal workpiece delivery temperature, and then uses this predicted force for setting the screwdowns in a way to compensate for the mill spring in order to produce the desired final plate thickness. An actual pass is then made through a stand, and any resulting thickness error is attributed to an erroneous workpiece temperature to improve and update the next pass roll force prediction and improve the workpiece reduction thereby.

FIG. 7 illustrates an example of this operation. This is a curve plot of roll separation force in millions of pounds versus final delivery plate thickness. The curved lines 60 and `62 at the right of the curve plot are the plastic characteristics of the product being rolled. The curves 64 :and 66 at the left of the curve plot are the mill spring characteristics. The point at which these two sets of lines intersect determines the thickness to be produced on any given pass. In the illustration shown in FIG. 7, the incoming thickness for pass N is .75 inch and the desired delivery thickness is .5 inch. Before pass N, the computer predicts the force to be about 6 million pounds and it sets the screwdown -for pass N at 0.315 inch. The plastic ch-aracteristic line 61 intersect the mill spring line 66 for the intended operation. The computer then sequences the mill to roll pass N, and in doing lso it measures the actual force to be only 5.8 million pounds and the result-ing thickness is only .49 inch, in accordance with the plastic characteristic line 60. The computer then recognizes this error and modifies the roll force equation to more accurately predict the force on the N+1 pass. The computer predicts a torce yot about. 4.9 million pounds for pass N+1 to reduce the thickness from .49 inch down to 0.375 inch, in accordance with plast-ic characteristic line 63 and mill spring line 64. In the actual rolling of pass N+1 the roll separating force in accordance with plastic characteristic line 62 is still less than the predicted value and consequently the gauge is slightly less than the desired delivery thickness of 0.375 inch.

As the Various parts of the rolling mill heat up and cool down and as the rolls wear, the slope of the mill spring lines or characteristics remain essentially constant, but the Zeroing of the screwdown positioning system must be changed periodically to compensate for dimensional changes -in the parts. This is done by monitoring the thickness of the rolled product with X-ray gauges and automatically recalibrating the screwdown positioning system prior to the last pass in the rolling of each piece. Manual adjustment is, of course, .possible if desired.

In FIG. 8, there is provided a diagrammatic showing of the present computer operation. FIG. 8 illustrates the input information received from the rolling mill, such as the measured workpiece temperature by the temperature gauge, the motor current, the motor voltage, the mill speed, the measured roll force and the strip speed. These are supplied through an analog to digital converter 10i) 'and an input buffer 102 and can pass through a priority and transfer control circuit 104 either to the memory unit 106 or the arithmetic unit 108 as is required. The backup roll diameter and the Work roll diameter are substantially constant and have a known variation in -accordance with the tons of workpiece rolled by the mill. This can be calculated by the computer as desired. The card reader 110 provides information such las the incoming workpiece dimensions, the material index, the desired wi-dth, the initial screwdown setting, the desired delivery gauge and the mill speed for ea-ch pass through the mill.

In FIG. 9, there is shown a curve illustrating the mill housing elongation plotted as a function of roll pressure. In accordance with the teachings of Shayne U.S. Patent No. 2,332,272 and others, the delivery thickness (h) is related to the total roll force (F) as shown in FIG. 9. The form of this curve will depend upon the width and thickness of the strip as these effect the .distribution of the loads applied to the rolls and the roll diameters as these effect the roll deflection for given applied loads. These dependences can be represented by a functional relationship of the form,

In most cases, the above equation can be placed in the form of Ithe following Equation 1 which is more convenient to work with. The act-ual curve is non-linear but approaches a linear form as the roll force increases.

In FIG. 10 there is provided a diagrammatic illustration of a tandem strip mill showing-stands 200 and 201 of a desired plurality of stands, with the succeeding workpiece passes, as previously discussed, being made in the succeeding stands of the mill. The roll force prediction operation for each stand is accomplished as previously described on :a sampling basis at each stand, and roll force predictions and screwdown setting determinations 'are -rippled along the travel path through the lmill stands in synchronism with the movement of the workpiece or strip. Workpiece thickness measuring gauges 202 and 204 and workpiece temperature measuring -gauges 205 and 268, as well as a roll force sensing -device 210, such as shown for stand 200, are provided for each stand to supply the necessary signals for controlling the rolled workpiece thickness in accordance with the teachings of the present invention. The delivery thickness and temperature gauges of a preceding stand supply the input control signals for the next succeeding stand.

In batch type processes wherein operations are sequentially performed on workpieces, if the operation requires a finite time period this allows lmeasurements to be taken during these operations. The input state of the metal piece to be rolled can be defined as a vector quantity having the numbers Xi: (X11, X21, X3i, Xni). The output state of the metal piece to be rolled can be defined as a second vector represented by a set of numbers There are constraints to be considered in the rolling mill operation in accordance withthe present invention, one of which is to control the roll force substantially in accordance with roll crown design to preserve the shape of the rolled workpiece and provide the desired flatness in terms of uniformity across the sheet without waviness and buckles. In addition, the mill motor cannot be overloaded, so motor torque must remain below some predetermined maximum value in accordance with the duty cycle of the motor to keep the motor from heating and below a safe value. The motor current limitation must be considered to modify the torque limits to conform with past duty cycle history of the mill motor to limit the mill motor heating. In addition, for a given workpiece material, the reduction in percentage of draft must be less than some specified value in accordance with past known rolling practices.

The following more detailed description of the teachings of the present invention will be in terms of, and relative to these equations and quantities, which can be empirically obtained as a refinement of existing theory and state of the art knowledge.

Equation 2-mN is a function of (WN, DN, dN) and is expressed by mN=mN (WN, DN, dN)

Equation 3--FN is a function of (HN, 1N 1, tN, VN, dN, DN, WN; M) and is expressed by FN=FN (HN, HN 1, N, VN, DN, WN, dni M) Equation 4-TN is a function of (1N 1, HN, tN, VN, DN;

In the above equations,

11N is -actual delivery plate thickness on the Nth pass SN is actual screwdown setting or roll separation on the Nth pass FN is actual roll separation force on the Nth pass mN is the mill spring parameter on the Nth pass WN is actual plate width on the Nth pass DN is actual mean diameter of work rolls on the Nth pass dN is actual mean diameter of backup rolls on Nth pass HN is desired plate thickness on Nth pass IN is actual mean plate temperature on Nth pass VN is work roll speed on Nth pass M is material composition index TN is motor torque on Nth pass It should be noted that the above equations two through four are empirical vector equations which can be readily established in specific form by any person skilled in this art through actual observation of the operational characteristics of the particular rolling mill to be controlled. The equation four is a constraint equation to limit the motor loading to a safe and predetermined maximum value. The general theory behind these empirical vector equations can be found in the published writings of Mr. Nadai and Mr. Orowan and others.

A reference here to U.S. Patent No. 2,332,272 of Shayne may be of interest. Shayne teaches the indication of rolled piece thickness (h) by combining a first signal (S) proportional to the setting of the screwdown mechanism and a second signal (F) proportional to roll separating force modified by the curve of mill stand elongation or mill spring characteristic (m).

A prior published article of interest relative to mill spring teachings for controlling the operation of a rolling mill is by Paul Blain in the Revue De Metallurgie, volume 45, No. 8, August 1948, on page 241.

A further reference of interest here is U.S. Patent No. 2,303,596 of Zeitlin, which describes a metal piece thickness measurement system utilizing screwdown setting (S), roll separation force (F) and the mill spring characteristic (m).

It is apparent that the term (FN/mN) in Equation 1 is simply the deflection of the rolls resulting from the strain of mill members imposed by the roll separating force (F). This deflection can be calculated with a fair degree of accuracy in the linear range using the stress/ strain formulas given by Timoshinko in his book on the Theory of Elasticity. A calculation of this kind was presented by M. D. Stone in his 1939 AISE Paper which can be refined to include the deflection of other mill members.

For a given mill, an accurate determination can be made experimentally in the following way. With the rolls turning and the mill empty, the screwdown mechanism is actuated to bring the work rolls together. Roll force is then provided by continued motion of the screwdown mechanism. The desired reaction is established by plotting measured roll force against roll separation as obtained from a translation through gear ratios and screwdown pitch from the measured angular movement of the screwdown mechanism. This measurement doesnot take into account the fact that mill deflection will also vary with the distance across the body of the roll over which the roll force will be applied. For example, the deflection of a beam will depend upon whether the load is applied at a point or distributed over some length of the beam. The deflection will then vary as a function of plate width (WN). This effect can be determined experimentally by rolling pieces of known thickness. By measuring the roll separation with the mill empty, and measuring the thickness of the rolled piece, the deflection for a measured roll force and piece width can be determined. In practice,A the diameters of the work and backup rolls will change due to wear. It is well known in the rolling art, that this wear is almost directly proportional to the tons of material produced. This usually occurs sufficiently closely that periodic measurements of roll diameters will provide sufficient accuracy although a computer can be used, if desired, to introduce corrections based on the total tonnage produced by the mill since the last roll change when the roll diameters were measured. Once the deflection versus roll force cu-rve, as shown in FIG. 9, is known for various values of WN, DN, and dN, an empirical equation, using conventional mathematical techniques can be used to flt an equation involving these variables to this data.

The calibration of the screwdown setting measurement will depend on the temperature of the mill members which will expand as their temperatures increase. Temperature variation will, therefore, introduce a null shift in the measurement of screwdown setitng (S). It is anticipated that nulling will be done when the mill is up to operating temperature. From this empirical equation, the function mN can be directly determined.

In regard to the above roll force Equation 3, the teaching of Von Karman, Nadai, yOrowan and Sims are per- 9 tinent as one suitable example to follow in the practice of this invention. The equation given by Orowan-Pascoe A second equation, given by Cooke and Larke based on the equation of Sims and using data obtained by them in compression tests is the following:

(7) F= Da-Henrad where D is effective roll diameter based on the well known Hitchcock formula. y

QF and Tap are given by curves in the Cooke and Larke work.

It is usually preferable, in place of the above theoretical expressions, however, to use data actually obtained on the mill to be controlled. For this purpose it can be more convenient to use the following subsidiary variables,

( 8 Hu H11-l rn -Hn 9 Hrm-'1 bn Dn (10) so that the roll force equation has the form (11) Fn=Fn rna bn, lnrNn; M)

One roll force equation that will serve as a specific example actually employed was:

A logarithmic form was used for convenience in the computer operation.

The material index represents the fact that the resistance to deformation of the plate will vary with plate material, i.e., low carbon, high carbon, alloy steel, etc. This merely means that a different equation would be used tor each type of material. It is anticipated, however, that one equation would fit several different materials so that lthe number of equations would not necessarily equal the number of dierent materials to be rolled. The roll speed in the latter formula was not significant for the operation performed. Data is accumulated for a large number of passes for which the quantities involved in the above equation are measured. A family of curves is then plotted and an empirical equation using conventional and well known mathematical methods is used to fit the curves. Alternately, the data could be stored in tabular form in the computer and roll force obtained by linear or polynomial extrapolation of the table entries. As a specific embodiment of this invention, it is assumed that the above Equation 3 has been obtained by empirical or other means as outlined above.

The computer can calculate the mill spring characteristic mN using above Equation 2 as a function of the width WN of the metal piece to be rolled, the diameter dN of the backup rolls and the diameter DN of the work rolls. Also this varies with roll wear but this is known and shouldbe treated as input data. In addition, if desired,

the mill spring characteristic m can be calculated by empirically passing several Workpieces through the rolling mill and actually measuring the delivery thickness lz and measuring the actual roll force and screwdown setting for each such pass. The mill spring characteristic m can then be determined by the formula 111:17 h-S.

Until the rolled workpiece delivery thickness lz becomes less than approximately 2 inches, when an X-ray thickness gauge is effective, based upon above Equation 1 the subsequently rolled me-tal piece thickness h can be calculated as being equal to the screwdown setting S plus the roll separation force F divided by the mill spring constant m. The computer can now determine the roll force FN for the Nth pass using above'Equation 3 as a predetermined vector function of the desired thickness HN of the workpiece for the Nth pass, the measured or calculated actual thickness hN 1 of the workpiece for the previous or Nl pass, the measured or de-termined temperature tN of the workpiece for the N pass, ythe speed VN or revolutions per minute of the work rolls for the N pass, the diameter DN of the work rolls, the diameter dN of the backup rolls and the material composition index M which is predetermined in accordance with the alloy composition ofthe workpiece in terms of carbon content, chromium content and the like. The exact form of this Equation 3 to ,use for the calculation of roll force can readily be determined by making several sample passes of workpieces through the controlled rolling mill and establishing the correct formula relationship by well known mathematical techniquesl Similarly, the computer can determine the motor torque T1 with above Equation 4 in terms of the desired thickness HN of the workpiece for the N pass, the measured actual thickness 1N 1 of the workpiece for the previous or (N 1) pass, the measured or determined temperature tN for the N pass of the workpiece, the speed VN of the work rolls and the diameter DN of the work rolls to establish the maximum torque limitation as a constraint for controlling the actual rolling mill operation. Motor torque is determined by field current and armature current. Speed is controlled by armature voltage and eld weakening. It is, in general, desirable to roll at maximum speed consistent with allowable motor torque requirements. Current limit is usually provided that will strengthen the field automatically if armature current exceeds allowable limits, but only up to rated full'ield current rating. Speed will decrease, if necessary, but this is generally undesirable since it is desired to maintain the speed per calculations. The computer sets motor speed and hence establishes torque available. Motor heating can be calculated on basis of a recorded history of well known motor loading characteristics assuming RMS value must remain below rating.

The servo system operative with the screwdown mechanism can set the initial screwdown calibration So by bringing the work rolls together to give a minimum roll separation force to bring the operation of the mill up to the linear portion of the characteristic curve as shown in FIG. 9 and as determined by the Equation 1 thickness formula /rzS-l-F/m previously set forth to thereby give the initial screwdown setting Se, and the feedback position transducer operative with the screwdown position control gives the absolute roll opening setting S as the feedback to the computer.

In general, the preliminary calculation of the schedule of passes for reversing mill operation is in accordance with already known practices, and as determined by above set forth objectives and constraints. Schedules of this type have already been calculated for reversing mills operative without control computers, and a generally similar approach is followed here. On the other hand, for a continuous tandem mill, the number of stands will determine the number of effective workpiece passes to be made.

The computer now calculates the predicted roll separation force F1 for the first pass using above Equation 3 in terms of the initially known data, including the incoming piece thickness ho, the desired thickness H1 of the metal piece at the end of pass l, the predetermined speed V1 of the work rolls as an input data from a punched card or other input media, the diameter D1 .of the work rolls, and the diameter d1 of the backup rolls, the temperature t1 of the incoming workpiece, the width W1 of the workpiece, and the material composition index M predetermined for the particular material to be rolled. Regarding the temperature t1 for the first pass, if the furnace temperature is 220G F. then a reasonable estimate for t1 could be 2l00 F. This calculation provides a predetermined target for the roll separation force F1 between the rolls. The computer now computes the screwdown setting S1 for the first pass using above Equation l in terms of the desired workpiece thickness H1 at the end of the first pass minus the computed first pass roll separation force F1 divided by the predetermined mill spring constant m in accordance with known rolling mill practice for the particular rolling mill under consideration. In this regard, the mill spring constant m has been computed and known in advance. Now the workpiece is passed through the rolling mill with the rolls driven at velocity V1 and the screwdown setting S1 being made, and the actual roll force F1 during the first pass is measured and, if feasible, the actual workpiece thickness lx1 at the end of the first pass is measured.

During the first few passes the workpiece thickness may be above 2 inches and too great for an X-ray gauge, and since the accuracies during the first few passes are not critical, the actual roll force F1 as measured by a roll force transducer can be utilized with the above thickness Equation l in terms of screwdown setting S and the reciprocal of the mill spring constant l/m times the measured roll force F1 for computing the actual workpiece thickness h1 delivered after the first pass.

The computer compares the target or desired workpiece thickness H1 after the first pass with the calculated actual workpiece thickness h1 after the first pass to determine any error. This error All in workpiece thickness, if outside a reasonable and permitted accuracy, is fed forward to the next pass to correct the predicted screwdown setting S for the second pass to more nearly arrive at the scheduled or desired workpiece thickness at the end of the second pass. It may be desirable to theoretically attribute this thickness error Ah to an incorrect evaluation of incoming workpiece temperature r1, since the workpiece temperature is very difficult to actually measure. We can now return to the above roll force Equation 3 F=F(H1, 1z0, t1, V1, D1, d1, W1; M) and compute the actual input temperature t1 for the first pass using the calculated workpiece thickness 111 at the end of the first pass, the measured roll separation force F1 of the first pass and the known speed V1 of the roll member to compute the input temperature t1.

The workpiece thickness, temperature and roll force values discussed above are average values, which are monitored and derived as desired over the total dimension of the workpiece or plate in the form of several readings, for example taken at one foot intervals, over the whole length of the workpiece in the direction of rolling.

Now the corrected temperature t1 of the workpiece can be used for determination of the roll force F2 and screwdown setting S2 for the second pass. In this regard, a compensated temperature value t2 for the second pass can be calculated based upon the previously calculated temperature t1 for the first pass, and modified to include time considerations regarding known temperature convection through the rolls, radiation from the workpiece into the air and conduction of heat through the air between the respective passes, as readily determinable from ernpirical temperature change information well known and obtainable by observation of actual rolling mill operation, such as shown in FIGS. 6 and 7.

Regarding the second pass of the workpiece through the rolling mill, it is known from the preliminary calculation of the predetermined number of passes desired through the mill to effect the desired thickness change for a reversing plate mill, or the number of stands for a tandem mill, what the desired workpiece thickness H2 at the end of the second pass should be, the actual thickness z1 of the workpiece entering the mill for the second pass corresponds to the actual thickness /11 delivered at the end of the first pass, the scheduled speed V2 of the rolls for the second pass is known. The incoming temperature t2 of the workpiece for the second pass has been calculated based upon the measured or calculated temperature of the workpiece for the first pass.

The previously discussed calculations are now repeated for the second pass by the computer. Namely, the roll force F2 for the second pass is calculated in terms of above Equation 3 as a function of the desired workpiece thickness H2 at the end of the second pass, the known actual incoming workpiece thickness h1 for the second pass, the computed temperature l2 of the workpiece incoming to the second pass, the known speed V2 of the work rolls, the known workpiece width W2, the known diameter d2 of the backup rolls, the known diameter D2 of the work rolls and the known material composition index M of the workpiece material. When the predicted roll force F2 for the second pass is calculated, the computer then computes the screwdown setting S2 for the second pass with above Equation l in terms of the desired delivery thickness H2 of the workpiece from the second pass minus as a quantity the predicted roll force F2 for the second pass divided by the known mill spring characteristic m. The screwdown setting is then made and the second pass is run.

The above described calculations are successively repeated for the subsequent desired number of passes or stands.

For at least the last pass or pass N, the X-ray gauge gives a direct and actual measurement of previous pass workpiece thickness /1N 1 to minimize errors due to calculated actual delivery thickness.

In general, it is desired to provide constraint limits on the passes of the workpiece through the rolling mill, since allowable reductions to prevent overloading of the mill motor and to prevent edge cracking and workpiece bending may not allow a full correction as calculated by the computer in any particular stand or next pass to be made. If the programmed passes will not allow the desired final delivery plate thickness, these constraint limits will cause the workpiece to be rolled to a final delivery thickness as close as practicable to the desired final thickness.

It should be noted for a reversing-plate mill that in accordance with conventional plate rolling mill operation, the screwdown mechanism cannot practically be adjusted during the course of any individual pass, so that feed forward of information for the purpose of predicting the roll force for the next succeeding pass and subsequently the screwdown setting for the next succeeding pass in accordance with the teachings of the present invention become very important. In the actual operation of a reversing plate mill, the initial workpiece length may be in the order of six feet, and may have a final length in the order of 1000 feet to provide up to only a minute or so of rolling time, since the speed of the workpiece through the mill may be in the order of 600 feet per minute up to 1000 feet per minute. Thusly, there is not sufficient time to change properly the screwdown mechanism during a given pass, so the preferred practice is not to employ a feedback of information for simultaneous and continuous monitoring of the workpiece thickness.

In general, input information for a given schedule is established from previous experience consistent with good drafting practice. This input information is supplied through the manual inputs and is given in part on punched data cards. The objective of the thickness control system in accordance with the present invention is to force previous pass.

13 the rolling mill to actually follow the desired schedules by proper setting of the mill screwdown mechanism. The proper initial width will be established preliminary to the workpiece entering the rolling mill. Since the amount of spread of the workpiece will be small, variations in width will either be neglected or translated into a equivalent temperature change automatically by the computer. The mill spring parameter m will be calculated in advance as a function of work roll diameter D, the backup roll diameter d and the sheet width W. This mill spring parameter m can be obtained by calibration made during the preceding schedule or pass if no change in the sheet width, the work roll diameter D and the backup roll diameter d occurs. In the alternative, it can be accomplished by deriving the mill spring parameter m as an empirical curve plotted in terms of screwdown setting as a function of roll force from the equation where lz is the actual delivery thickness from a plurality of preceding passes through the mill as measured by an X-ray gauge or any suitable thickness gauge, S is the screwdown setting for those passes and F is the measured roll separation force for those passes. `The curve of mill spring parameter m is now stored in the computer memory. The material composition index M is stored in the computer memory. The width of the workpiece W is stored in the computer memory; The screwdown position S for the previous pass is stored in the computer memory. The delivery thickness h for the previous pass is determined or measured and then stored in the computer memory, as is rolling speed V of the mill for the The backup roll diameter d and work roll diameter D are manually entered into the computer for storage in the computer memory.

The main mill motor is now accelerated to the desired operating roll speed according to instructions received from the punched card and the workpiece is introduced to the mill after proper alignment. Samples of the actual roll separation force are taken for each pass approximately at equal intervals of the work strip, for example every two feet apart, and the average of the measured roll separation force is thereby obtained and stored in the computer memory.

Between the first pass andthe second pass the delivery thickness h1 of the workpiece after the first pass is calculated from the formula h1=S1+F1/m, where h1 is the delivery thickness of the workpiece from the first pass, S1 is the measured screwdown setting for the rst pass, and m is the known mill spring parameter precalculated and F1 is the average roll separation force measured for the first nass.

During the second pass the substantially same operations that were operated before and during the tirst pass will be performed again, such that the screwdowns will be positioned in accordance with instructions of the scheduled second pass and so forth. In the operationsbetween the second and third passes, the actual delivery thickness of the second pass h2, which is the same as the entry thickness of the following pass, is calculated from the Equation l formula h2=S2|F2/m.

The effective temperature of the second pass will be calculated by means of the Equation 3, where the effective temperature t2 is a function of the first pass delivery thickness h1, second pass thickness H2, the work roll diameter D, the backup roll diameter d, work roll speed V2, plate or strip width W, material index, and measured roll force F2 for the second pass.

The roll force F3 for the third pass is calculated by means of empirical vector Equation 3. There are three possible values of the screwdown setting S3 for the third pass. The first value would be the prescheduled value of screwdown setting specified by the punched card. The second value would be the maximum value limited by equipment capacity such as maximum permissible roll force, maximum permissible reduction and the maximum permissible motor torque.v In addition, the third value of screwdown setting can be calculated in accordance with Equation 1 previously set forth S=h-F/m. If the calculated value is greater than the maximum permissible value, the maximum permissible value will be used and an indication is given to the operator of possible fault. If the calculated value of screwdown setting is less than the maximum and greater than the punched card or prescheduled value, the screwdowns will be set according to the calculated value.

The operations for the next succeeding pass and the following passes will continue in a similar manner until the pass for which the specified delivery thickness is less than two inches, when the X-ray thickness gauge is operative to measure actual workpiece thickness unless the operator decides to take over the responsibility of workpiece gauge control due to the continued indication of possible calculated gauge inaccuracy as mentioned above.

During the last pass for which the specified delivery thickness is larger than two inches, the operations for this particular pass will be the same as for` previous passes, except one additional operation is initiated by means of internal programming. This additional operation is such that during this pass and before the next subsequent pass the X-ray gauge to be used on the following pass is standardized for this prescribed delivery thickness for the subsequent pass.

For the first pass of the workpiece through the rolling mill rfor which the delivery thickness is two inches or less, instead of using roll force to calculate actual delivery thickness h, the latter quantity will be directly measured by means of the proper X-ray gauge mounted on the side of the mill to which the sheet is being delivered. In addition, the mill spring parameter m is evaluated after this pass by the formula i h-s and stored for future use in the just succeeding schedule if no change in the specification occurs. The operations for the last two passes will be the same as the previous pass except the mill spring parameter m will be stored only for reference purposes.

In the practice of the present invention, there are two different ways to operate the computer and mill control apparatus.

(A) Preprogrammed number of passes. (B) Not preprogrammed number of passes.

In accordance with operation (A), the desired number of passesof the workpiece through the mill is scheduled or programmed in advance, such that the roll force and screwdown setting calculations herein described are utilized to more accurately comply with the scheduled workpiece thickness targets for the respective passes. The motor torque calculation is operative as a constraint to prevent overloading and resulting overheating of the mill motors. Also, the reduction taken in terms of percent draft must be held below Well known values to conform with conventional and accepted r-olling mill operative practices.

In accordance with operation (B), the number of passes through the rolling mill is not scheduled in advance but instead the rolling mill electrical and mechanical components are fully loaded up to the maximum predetermined limits therefor, to in effect optimize the utilization of the rolling mill apparatus to obtain the maximum production of quality product. Here the torque constraint, and other operational limitations such as motor current and percentage draft, are always brought up to their practical limits to in effect fully load the rolling mill in its performance. Another important consideration readily apparent to persons skilled in this art is that the `final pass of the workpiece must effect a delivery in the desired direction from the proper side of the rolling mill.

For both of operations (A) and (B), the roll separation force Equation 3 is empirically determined for the particular mill to be controlled by a preliminary operation to actually measure the involved quantities of Equation 3 and then determining by well known mathematical principles the exact form of Equation 3 to satisfy those measured quantity values. For each successive pass in the subsequent production operation, the roll force F is then predicted by calculation to in turn determine a predicted screwdown setting S. The workpiece is passe through the rolling mill with this screwdown setting S held constant. The actual roll force F is measured, and the actual delivery thickness l1 is measured for that pass. Using the measured roll force F, the workpiece temperature t-is calculated using Equation 3, and any error in actual workpiece thickness as compared to the desired workpiece thickness for that particular pass is attributed to an error in the workpiece temperature used for the prediction by calculation of the roll force F for that same pass. This is done since the workpiece temperature is very difficult to actually measure on a pass to pass basis, so a calculation of workpiece temperature is made following each pass to be fed forward after compensation for known losses to allow a more accurate calculation of the roll force for the next succeeding pass of the workpiece through the rolling mill.

The card reader 42 is operative to supply to the cornputer 24 as input data the material index M, the workpiece width W, the pass number N to be performed, the scheduled screwdown setting S for each pass, the desired delivery gauge H for each pass and the `scheduled roll speed V for each pass. The computer already has stored in its memory the roll diameter D and the backup roll diameter d. The incoming workpiece thickness or gauge lzo for the first pass can be supplied by the card reader 42 -or the manual inputs 40 as may be desired; the same is true for the temperature t. The provided thickness gauges 31 and 34 and the provided temperature gauges 36 and 38 are operative for the supply of of this information as may be desired, particularly between the successive passes of the workpiece through the rolling mill 10. The lactual roll force signal is measured by the roll force transducer 37. The actual speed of the roll 14 is measured by the speed sensing transducer 39.

The starting and stopping of the various motors can be performed by the computer 24 in conjunction with the conventional mill control apparatus 26 as readily apparent to persons skilled in this particular art. The conventional mill control apparatus 26 may be desirable for pattern speed control and screwdown control purposes and for the initial rolling of the workpiece to establish the desired width W prior to making a 90 turn and beginning the thickness control operation of the rolling mill 10 in accordance with the teachings of the present invention.

If one or both of the entry and delivery thickness gauges 31 and 34 respectively, are Iout of service, for example the entry gauge 31 lis out of service, the measured roll force F will continue to be used for determining the delivery thickness on the entry side of the mill. The mill spring parameter m will again be evaluated during the next to the last pass to determine a more accurate calibration of entry thickness for the last pass. If the delivery gauge 34 is out of service, the measured roll force will continue to be used for calculating delivery `thickness on the delivery side of the mill. However, if the delivery gauge 34 is out of service, the indication of final actual delivery thickness will not be obtainable.

If both thickness gauges are out of service, the roll force determination alone will be used and the mill spring parameter m will be calculated from the Equation 2 m=m(W, D, d).

It is intended that the temperature gauges 36 and 38 16 and the thickness gauges 31 and 34 shown in FIGURE l be utilized when suitable during the operation of the rolling mill to tinalize the empirically determined rolling vector equations previously set forth. In general, the values of the parameters in these vector equations will be more accurately determined in this manner.

A plurality of force curves can be plotted as a function of r for reduction. Each material index gives a separate force curve in this regard. This data is obtained during preliminary running the rolling mill and then optimizing the data to fit mathematically for least squares and the like. Now the vector equation is solved for temperature. In terms of the quantity b, defined as the square root of the input thickness divided by roll diameter for a rolling mill, and the reduction quantity r, delined as the input thickness minus the output thickness divided by the input thickness, a family of curves can be plotted whereby the percent reduction is varied for each value of b.

Now for 4the first pass, the predicted rollv force F1 is calculated, and this then enables the calcul-ation of the screwdown setting. The rolls are set to this and the piece entered in the mill and passed through the mill. The actual roll force is measured and any difference in roll force between the predicted roll force and the actual roll force is noted. However, if the predicted roll force equals the measured roll force, and the desired delivery thickness equals to the measured delivery thickness, the operation is on target. However, for any errors, the assumption is made that `the workpiece temperature utilized in the vector equations was wrong and by working backwards through the equations, a more realistic actual temperature -can be calculated, which if initially used would have provided the desired delivery thickness corresponding to the actual delivery thickness from the first pass. For the next pass, an estimated change in the temperature is made to calculate a new workpiece temperature, and if the desired delivery thickness from the second pass does not correspond to the actual delivery thickness -of the second pass, it is assumed that the latter calculated temperature was in error. In this manner, a plot of workpiece temperature as a function of time can be provided by a plurality of readings, and a curve can be provided for future consideration in the making of the temperature change estimates.

In the operation of the apparatus shown in FIG. 8, the input information through the card reader and the workpiece temperature are utilized to initially determine the screwdown setting. The workpiece is introduced into the mill and the mill is accelerated. During the actual pass, samples are made of the roll force and workpiece temperature for every two feet of the strip as indicated by a provided pulse wheel or the like and laverages are made of these quantities. After the first pass, the computer is operative to compute the delivery gauge. Then a calculation is made of the screwdown setting for the second pass, the mill is reversed and the workpiece is introduced into the mill and the mill is accelerated. During the second pass, samples are made of the roll force and workpiece temperature in a manner similar to that performed during the rst pass.

In the provision of strip thickness control apparatus for a continuous tandem mill in accordance with the present invention, the transport time delay required for a given increment of workpiece to travel from a preceding stand to a succeeding stand must be considered. In FIG. 1l there is shown one' form of control apparatus suitable for this purpose. A preceding stand 300 is equipped with the necessary interstand transducers and sensing devices to provide an actual roll force signal, workpiece or strip travel speed signal, and work strip thickness and temperature signals if practicable, to an interstand computer dc- Vice 302 operative to calculate the corrected temperature of the work strip at stand 300, if the actual delivery thickness 0f the work strip out of stand 360 is in error compared to the desired thickness. Using this corrected work strip temperature, the predicted roll force for the succeeding stand 304 is calculated and from this the desired screwdown setting for stand 304. The latter screwdown setting is entered into a memory and shift register 306 operative with a work strip travel speed signal from a pulse wheel or the like device 303, such that the stored screwdown setting is caused to shift through the register in synchronism with the movement of the associated work strip increment, for example a finite length of one foot, between stand 300 and stand 304. This stored screwdown setting is then fed to the screwdown control 3ll0 for the stand 304 in the proper time schedule to correspond with the passage of the associated work strip increment through the succeeding stand 304. In this manner successive screwdown settings are determined and applied to the succeeding stands in the proper time schedule to provide a final delivery thickness in accordance with a predetermined and desired value.

During the passage of each finite length or increment of work strip through any particular mill stand there is an average taken of the increment roll force, the increment temperature, the increment thickness and the incrernent travel speed for the purposes of the above described strip thickness control operation. At the delivery side of the last mill stand 320 there is provided an X-ray thickness measuring gauge 3Zl to supply a strip thickness signal to a master computer 322 for controlling the operational level of the illustrated control apparatus. Thusly, if the cumulative screwdown settings and rolling operations as provided by the respective computer devices operative between the mill stands, such as the computer device 302,' do not deliver a work strip from the last stand 320 having the desired final thickness, the X-ray gauge 321 can provide an operation correcting thickness signal to adjust the respective calculations made by the individual computer devices between the stands of the rolling mill, such as computer device 302.

In FIG. l2 there is shown a curve plot illustrating the work strip temperature changes that can be measured at a given stand for the whole length of strip passed through that stand, for example the stand 300 shown in FIG. l1. The curve 340 shows the temperature variation along the work strip as a function of time such as could be measured at a mill stand through which the work strip passes. The curve 342 illustrates the theoretical temperature variation of the same work strip such as could be measured at the next succeeding stand 304, as shown in FIG. 1l, if there were no drop in temperature clue to known heat losses in passing between these mill stands. However, in actual practice the curve 344 more accurately represents the actual work strip temperature variation as a function of time when taken at the next succeeding stand 304. The time interval shown as AT represents the work strip movement transport time between the mill stands 300 and 304. The information provided by the curve plot of FIG. l2 can be utilized by the computter devices shown in FIG. 11 to introduce the necessary temperature changes when determining the work strip temperature at the next succeeding stand for predicting the roll force and then the screwdown setting for that next succeeding stand to result in the delivery of the work strip at an actual thickness substantially the same as the desired thickness for that next succeeding stand. If desired, it should be noted that analog computer devices in the form of operational amplifiers are suitable for the generation of the screwdown signals for the next succeeding mill stand including the required time delay to permit synchronization with the travel of the work strip.. Suitable analog memory storage is well known in this art and available at the present time in the form of switched, storage capacitors.

In the operation of the apparatus shown in FIG. l-l, it is assumed that the work strip Width remains substantially constant. The first stand input temperature T1 of any given work strip increment is estimated from the known and measured furnace operation and previous eX- perience in moving Asimilar workpieces from the furnace into the first stand of the rolling mill. This empirical work strip temperature estimate T1 can be supplemented by reasonably accurate and reliable improved actual temperature sensing devices, if available, and these would allow the first stand operation itself to be better controlled in accordance with the present invention. For a given finite increment of the work strip passing through the first stand, the average actual roll force F1 and average screwdown setting S1 are measured, the strip speed is measured, and the average temperature T1 is either measured if practicable orV calculated correctly to compensate for any difference between the actual work strip thickness and the desired work strip thickness, assuming that such difference is attributable to an error in the estimated input temperature T1 to the first stand.

The computer device 302 now calculates the estimated temperature T2 of the same given finite Aincrement of work strip relative to the second stand 304, and then uses this estimated temperature T2 to predict the roll force F2 required to provide the desired work strip thickness from the second stand 304. The predicted roll force F2 is used to calculate the screwdown setting S2 for the second stand 304, and this screwdown setting S2 is entered into the memory and shift register to be synchronized by the strip speed with the travel movement of the given finite increment from the first stand 300 to the second stand 304. As this same given increment of work strip passes throughlthe second stand 304, the average roll force F2 and average screwdown setting S2 are measured, the speed of the strip between stand 304 and the next succeeding stand is measured, and the average temperature T2 is either measured if practicable or calculated correctly to compensate for any resulting thickness difference on the assumption that it Was caused by an error in the estimated temperature T2.

The computer device following the second stand 304 now calculates the estimated temperature T3 of the same finite increment of work strip for the control of the third stand, and then predicts the roll force F3 required to provide the desired work strip thickness from the third stand. The screwdown setting S3 is now determined and is delayed in time to permit the travel of this same given finite increment to the third stand. It should be understood that any necessary screwdown adjustment time period is included as part of the -provided time delay such that the third stand screwdown setting is in fact the desired setting S3 for the passage of the given increment of work :strip through the third stand.

The successive stands of the rolling mill are similarly controlled. The final delivery thickness is measured by an X-ray gauge to provide any desired control system level adjustments deemed to be desirable and necessary. Sequential entering of thickness control signals into interstandvmemory device is provided. For example, if there are eighteen feet of moving strip between stand 300 and stand 304 shown in FIG. 11, for each foot increment of strip there will be entered into the interstand memory device the thickness control information needed to cause the next succeeding stand 304 to effect any desired correction in the strip thickness of the same foot increment of strip and as determined by measurements made at stand 300 relative to that same foot increment of strip.

The information stored in the interstand memory demanner in synchronism with the travel movement of each strip increment through the successive stands of the continuous tandem mill.

It should be readily apparent to those skilled in this particular art that magnetic core or similar well known memory devices are well suited to the storage and coordination of this strip thickness of control information.

While the present invention has been described in particular embodiments thereof and in particular use, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the present invention.

I claim as my invention:

1. The method of controlling the thickness of a plurality of increments of a workpiece moving in a succession of passes through roll members, with the separation force between said roll members for each of said passes being controlled by a screwdown mechanism, comprising the steps of predicting a first pass roll separation force for each of said increments in accordance with a predetermined relationship with at least the incoming thickness of each corresponding increment of the workpiece, the desired delivery thickness of each corresponding increment of the workpiece, and the estimated temperature of each corresponding increment of the workpiece; determining a first pass screwdown position setting for each said increment in accordance with a predetermined relationship with at least said predicted first pass roll separation force for each said increment; making a first pass of each increment of the workpiece between said roll members with said screwdown mechanism positioned in accordance with said first pass screwdown position setting for each said increment; measuring the actual roll separation force for each increment during said first pass; determining the actual delivery thickness for each increment of the workpiece from said first pass and the actual temperature of each increment of the workpiece in accordance with the first pass actual roll separation force; predicting a second pass roll separation force for each workpieceincrement in accordance with said first pass actual delivery thickness and the first pass actual temperature of each increment of the workpiece; determining a second pass screwdown position setting for each workpiece increment in accordance with a predetermined relationship with at least said second pass roll separation force; storing the second pass screwdown position setting for each workpiece increment; making a second pass of each increment of the workpiece between said roll members with said screwdown mechanism positioned for each workpiece increment in accordance with said second pass screwdown position setting; and synchronizing the movement of each Iincrement of said workpiece in said succession of passes with the storing of the second pass screwdown position setting such that a desired time delay is introduced in accordance with said workpiece movement.

2. The method of controlling the thickness of each increment of a moving workpiece passed through a rolling mill between rolls, with the separation force between each pair of rolls being controlled by a screwdown mechanism, comprising the steps of predicting a first pass roll separation force for said increment in accordance with an empirically predetermined relationship with at least the first pass incoming thickness of the workpiece increment, the first pass desired delivery thickness of the workpiece increment, and the first pass temperature of the workpiece increment; predicting a first pass screwdown position setting for said workpiece increment in accordance with a predetermined relationship with the desired delivery thickness of the workpiece increment, said predicted first pass roll separation force for said increment and a predetermined mill spring characteristic for said rolling mill; passing the workpiece increment through said rolling mill between said rolls after the screwdown mechanism has been positioned in accordance with said predicted first pass screwdown position sett-ing for said increment; determining for the first pass for said increment the actual roll separation force, the actual delivery thickness and the temperature; predicting a second pass roll separation force for said workpiece increment in accordance with said predetermined relationship with a least the second pass incoming thickness of said increment, the second pass desired delivery thickness of said increment and the second pass temperature of said increment; predicting a second pass screwdown position setting for said increment in accordance with said predetermined relationship with the desired second pass delivery thickness of said increment, the predicted second pass roll separation force for said increment and a predetermined mill spring characteristic for said rolling mill; and delaying the control of said screwdown mechanism by said second pass screwdown position setting until the workpiece increment has moved into position to make the second pass through the rolls.

3. The method of controlling the delivery thickness of a workpiece increment during each of a plurality of passes through a pair of rolls, with the desired delivery thickness of said workpiece increment after each of said passes being predetermined and with the separation force between said rolls being controlled by a screwdown mechanism, comprising the steps of predicting for each successive pass of the workpiece increment the roll separation force in accordance with a predetermined relationship with the incoming thickness of the workpiece increment for that pass, the desired delivery thickness of the workpiece increment for that pass, the temperature of the workpiece increment for that pass, the speed of the rolls for that pass, the diameter of the rolls, and a predetermined material composition index for the workpiece; predicting a screwdown position setting for the workpiece increment for each pass in accordance with a predetermined relationship with the desired delivery thickness of the workpiece increment for that pass, said predicted pass roll separation force and a predetermined mill spring characteristic for said rolling mill; successively passing the workpiece increment through said rolling mill between said rolls with said screwdown mechanism positioned in accordance with said predicted screwdown position setting for each of said predetermined number of passes; sensing the movement of the workpiece increment between each of said passes; and delaying the control of the screwdown mechanism for each pass in accordance with the movement of the workpiece increment.

4. The method of controlling the thickness of a moving workpiece increment making at least two passes through a rolling mill having rolls, with the desired delivery thickness of said workpiece increment after each of at least said two passes being predetermined, and a screwdown mechanism being provided to control the relative positions of each pair of rolls, comprising the steps of estimating a first pass roll separation force for said workpiece increment in accordance with a predetermined relationship with at least the known incoming thickness of the workpiece increment, the first pass desired delivery thickness of the workpiece increment, the first pass temperature of the workpiece increment; estimating a first pass screwdown position setting for said increment in accordance with a predetermined relationship with at least the desired delivery thickness of the workpiece increment after said first pass and said estimated first pass roll separation force; passing the workpiece increment between a pair of said rolls with said screwdown mechanism being positioned in accordance with said estimated first pass screwdown position setting during this first pass; determining the actual first pass roll separation force and the actual delivery thickness of said workpiece increment after the first pass; determining a corrected second pass temperature of said workpiece increment in accordance with a third predetermined relationship with at least the first pass incoming thickness of the workpiece increment, the first pass actual delivery thickness of the workpiece increment, and the actual first pass roll separation force; estimating second pass roll separation force in accordance withl a predetermined relationship with at least the second pass incoming workpiece increment thickness, the second pass desired delivery workpiece increment thickness and thecorrected second pass temperature of the workpiece increment; sensing the movement of the workpiece increment; and controlling a screwdown mechanism for a pair of rolls in accordance with said second pass roll separation force in synchronism with the passage of said workpiece increment between the latter pair of rolls for controlling the thickness of said workpiece increment after the completion of at least said two passes through the rolling mill.

5. The method of controlling the thickness of a mov ing workpiece increment successively operated upon by thickness control means including separated force providing means, comprising the steps of effecting a first operation upon said workpiece increment by said thickness control means; determining the temperature of said workpiece increment during said first operation in accordance with a predetermined relationship to at least the force provided by said force providing means, the entry thickness of said workpiece increment and the delivery thickness of said workpiece increment for said first operation; predicting the force required by said force providing means for a second operation upon said workpiece increment in accordance with a predetermined relationship to at least said workpiece lincrement temperature and the workpiece increment entry thickness and desired workpiece increment delivery thickness for said second operation; determining a second operationseparation for said separated force providing means in accordance with said second operation predicted force; sensing the movement of the workpiece increment; and effecting a second operation upon said Iworkpiece by said thickness control means after a time delay in accordance with the movement of the workpiece increment.

6. The method of controlling the thickness of a moving .workpiece increment through successive operational passes by thickness control means including separated force providing means, comprising the steps of operating upon said workpiece increment by thickness control means; measuring the force provided by said force providing means during that operation; determining the temperature of the workpiece increment during that operation by a known relationship with the operation measured force, the operation entering workpiece increment thickness and the operation delivery workpiece increment thickness; successively deter-'mining the desired `force to be provided by force providing means during each successive operation upon said workpiece increment from a known relationship with the previous operation temperature, the successive operation entering workpiece increment thickness and the successive operation delivery workpiece increment thickness; successively determining the separation setting for said force providing means during each successive operation from a known relationship with said determined desired force and the successive operation delivery workpiece increment thickness; sensing the 4movement of the workpiece increment through said thickness control means; and synchronizing the successive operations upon said workpiece increment by said thickness control means using said successively determined separation setting for the separated force providing means.

7. In apparatus for controlling the thickness of a workpiece moving in a succession of passes through the roll members of a rolling mill, with the separation betiween each pair of roll members being controlled by a screwdown mechanism, first control means operative with the screwdown mechanism for the first pass roll members for providing a first pass separation setting for each predetermined increment of the workpiece; rst signal providing means operative with said first pass roll members during the first pass `for providing for each predetermined increment of the workpiece at least an actual roll force signal, an actual delivery thickness signal and an actual temperature signal; second control means operative with the screwdown mechanism for the second pass roll members for providing a second pass separation setting for each predetermined increment of the workpiece in accordance with at least the corresponding actual delivery thickness signal and actual temperature signal; second signal providing means operative with the respective increments `of the workpiece for providing a movement signal for each workpiece increment; with the second control means being responsive to said movement signal for each increment for synchronizing the second pass separation setting for each tworkpiece increment with the corresponding workpiece increment as it moves through the roll members of said rolling mill.

8. In apparatus for controlling the thickness of a workpiece moving in a plurality of successive passes through the roll mem-bers of a rolling mill, with the separation between each pair of roll members being controlled by a screwdown mechanism, first control means operative with the screwdown mechanism for the first pass roll members for providing a first pass separation setting for each predetermined increment of the workpiece; first signal providing means operative with said rst pass roll members to provide for each said increment of the workpiece at least an .actual delivery thickness signal and an actual temperature signal; second control means operative with the screwdown mechanism for the second pass roll members for providing a second pass separation setting for each said increment of the workpiece in accordance with at least the correspondnig actual delivery thickness signal and actual temperature signal; second signal providing means operative with said increments of the workpiece for providing a movement signal for each workpiece increment; with the second control means being responsive to said movement signal for each said increment for synchronizing the second pass separation setting for the corresponding workpiece increment as it moves through the second pass roll members of said rolling mill.

9. In apparatus for controlling the thickness of a workpiece moving in a succession of passages through the roll members of a rolling mill, with the separation between the roll members for each said passage being controlled by a screwdown mechanism, first control means operative with the screwdown mechanism for the roll members for a given passage to provide a given passage separation setting for each predetermined increment of the workpiece; first signal providing means operative with said workpiece during said given passage for providing for each said increment of the workpiece at least an actual delivery thickness signal and an actual temperature signal; second control means operative with the screwdown mechanism for a succeeding passage roll members for providing a succeeding passage separation setting for each predetermined increment of the workpiece in accordance with at least said given passage actual delivery thickness signal and said given passage actual temperature signal for the corresponding workpiece increment; second signal providing means operative with the respective increments of the workpiece for providing a movement signal for each workpiece increment and delayed in time in accordance with the movement of that increment; with the second control means being responsive to said movement signal for each workpiece increment for synchronizing the succeeding passage separation setting with the corresponding workpiece increment as it moves through the succeeding passage roll members of said rolling mill.

10. In apparatus for controlling the thickness of a workpiece strip moving through successive stands of a rolling mill, with the separation between each stand roll members being controlled by a screwdown mechanism, first control means operative with the screwdown mechanism for the first stand for providing a first stand roll member sepa- 23 ration setting for each predetermined increment of the workpiece strip; rst signal providing means operative with `said rst stand for providing for each predetermined increment of the workpiece strip at least an actual delivery thickness signal and an actual temperature signal; second control means operative with the screwdown mechanism for 4the second stand `for providing a second stand roll member separation setting for each predetermined increment of the workpiece strip in accordance with at least the tirst stand actual delivery thickness signal and the :first stand actual temperature signal for the corresponding increment; second signal providing means operative with the respective increments of the workpiece strip for providing a movement signal for each workpiece strip incre-ment; with the second control means being responsive to said movement signal for each increment for synchronizing the Isecond stand roll member separation setting ywith the corresponding workpiece stnip increments as they move through the second stand of said rolling mill; and third signal providing means operative with the workpiece strip increments as they leave the rolling mill for providing a predetermined thickness error signal operative with at least one of the first control means and the second control means to control the delivery thickness of the workpiece strip from the rolling mill.

11. In apparatus for controlling the thickness of a workpiece strip moving through succeeding stand roll members of a rolling mill, with the lseparation between each stand roll members being 'controlled by a screwdown mechanism, first control means operative with the screwdown mechanism for a preceding stand roll members for providing a preceding stand separation setting for each predetermined increment of the workpiece strip; rst signal providing means operative with the workpiece strip while between said preceding stand roll members for providing ifor each predetermined increment of the workpiece strip at least an actual delivery thickness signal and an actual temperature signal; ysecond control means operative with the screwdown mechanism -for a succeeding stand roll members for providing a succeeding stand separation setting for each predetermined increment of the workpiece in accordance with at least the corresponding increment actual delivery thickness signal and actual temperature signal; second signal providing -means operative with the respective increments of the workpiece for providing a movement signal for each workpiece increment; and interstand signal storage means operative with the second control means and being responsive to said movement signal for each increment for correlating the succeeding stand separation setting with the movement of the corresponding workpiece increment through the succeeding stand roll members of said rolling mill.

References Cited by the Examiner UNITED STATES PATENTS 2,659,154 11/1953 Rendel 73-88.5 2,767,604 10/1956 ,Whalen 72-13 3,015,974 l/196-2 Orbom et al. 72-9 3,062,078 11/1962 Hulls 72-9 3,104,566 9/1963 Schurr et al. 72--8 3,128,630 4/1964 Briggs 73-432 CHARLES W. LANHAM, Primary Examiner.

C. H. HITTSON, Assistant Examiner. 

1. THE METHOD OF CONTROLLING THE THICKNESS OF A PLURALITY OF INCREMENTS OF A WORKPIECE MOVING IN A SUCCESSION OF PASSES THROUGH ROLL MEMBERS, WITH THE SEPARATION FORCE BETWEEN SAID ROLL MEMBERS FOR EACH OF SAID PASSES BEING CONTROLLED BY A SCREWDOWN MECHANISM, COMPRISING A STEPS OF PREDICTING A FIRST PASS ROLL SEPARATION FORCE FOR EACH OF SAID INCREMENTS IN ACCORDANCE WITH A PREDETERMINED RELATIONSHIP WITH AT LEAST THE INCOMING THICKNESS OF EACH CORRESPONDING INCREMENT OF THE WORKPIECE, THE DESIRED DELIVERY THICKNESS OF EACH CORRESPONDING INCREMENT OF THE WORKPIECE, AND THE ESTIMATED TEMPERATURE OF EACH CORRESPONDING INCREMENT OF THE WORKPIECE; DETERMINING A FIRST PASS SCREWDOWN POSITION SETTING FOR EACH SAID INCREMENT IN ACCORDANCE WITH A PREDETERMINED RELATIONSHIP WITH AT LEAST SAID PREDICTED FIRST PASS ROLL SEPARATION FORCE FOR EACH SAID INCREMENT; MAKING A FIRST PASS OF EACH INCREMENT OF THE WORKPIECE BETWEEN SAID ROLL MEMBERS WITH SAID SCREWDOWN MECHANISM POSITIONED IN ACCORDANCE WITH SAID FIRST PASS SCREWDOWN POSITION SETTING FOR EACH SAID INCREMENT; MEASURING THE ACTUAL ROLL SEPARATION FORCE FOR EACH INCREMENT DURING SAID FIRST PASS; DETERMINING THE ACTUAL DELIVERY THICKNESS FOR EACH INCREMENT OF THE WORKPIECE FROM SAID FIRST PASS AND THE ACTUAL TEMPERATURE OF EACH INCREMENT OF THE WORKPIECE IN ACCORDANCE WITH THE FIRST PASS ACTUAL ROLL SEPARATION FORCE; PREDICTING A SECOND PASS ROLL SEPARATION FORCE FOR EACH WORKPIECE INCREMENT IN ACCORDANCE WITH SAID FIRST PASS ACTUAL DELIVERY THICKNESS AND THE FIRST PASS ACTUAL TEMPERATURE OF EACH INCREMENT OF THE WORKPIECE; DETERMINING A SECOND PASS SCREWDOWN POSITION SETTING FOR EACH WORKPIECE INCREMENT IN ACCORDANCE WITH A PREDETERMINED RELATIONSHIP WITH AT LEAST SAID SECOND PASS ROLL SEPARATION FORCE; STORING THE SECOND PASS SCREWDOWN POSITION SETTING FOR EACH WORKPIECE INCREMENT; MAKING A SECOND PASS OF EACH INCREMENT OF THE WORKPIECE BETWEEN SAID ROLL MEMBERS WITH SAID SCREWDOWN MECHANISM POSITIONED FOR EACH WORKPIECE INCREMENT IN ACCORDANCE WITH SAID SECOND PASS SCREWDOWN POSITION SETTING; AND SYNCHRONIZING THE MOVEMENT OF EACH INCREMENT OF SAID WORKPIECE IN SAID SUCCESSION OF PASSES WITH THE STORING OF THE SECOND PASS SCREWDOWN POSITION SETTING SUCH THAT A DESIRED TIME DELAY IN INTRODUCED IN ACCORDANCE WITH SAID WORKPIECE MOVEMENT. 